[BUG] refcount saturation in qrtr_port_assign during qrtr_proto_init

Dear Developers,
I am reporting a refcount_t: saturated bug in the QRTR protocol stack found via Syzkaller on Linux 6.18.0. 

Analysis: The issue occurs during the initialization of the QRTR protocol. When qrtr_ns_init calls kernel_bind, the execution flow reaches qrtr_port_assign which calls sock_hold. It seems the refcount of the socket object increments unexpectedly until saturation. 

Log highlights:
WARNING: refcount_warn_saturate+0x94/0x170
Call Trace: qrtr_port_assign -> __qrtr_bind -> qrtr_bind -> kernel_bind -> qrtr_ns_init
Environment:
Kernel: 6.18.0 #5 PREEMPT(none)
Arch: x86_64 (QEMU)
Full dmesg log is attached below.
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	3-...!: (4 ticks this GP) idle=5944/1/0x4000000000000000 softirq=164244/164245 fqs=0
rcu: 	(detected by 2, t=10502 jiffies, g=240157, q=469 ncpus=4)
Sending NMI from CPU 2 to CPUs 3:
NMI backtrace for cpu 3
CPU: 3 UID: 0 PID: 62625 Comm: syz.3.16293 Not tainted 6.18.0 #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:lock_release+0x13/0x2f0 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/lockdep.c:5876
Code: 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 49 89 f4 55 48 89 fd <48> 83 ec 18 65 48 8b 05 a9 24 eb 11 48 89 44 24 10 31 c0 0f 1f 44
RSP: 0018:ffffc90002da7558 EFLAGS: 00000082
RAX: dffffc0000000000 RBX: 0000000000000046 RCX: ffffffff8197192b
RDX: 1ffff1100c504fa0 RSI: ffffffff81a6e607 RDI: ffff888062827c98
RBP: ffff888062827c98 R08: 0000000000000001 R09: fffff520005b4ea2
R10: 0000000000000003 R11: 0000000000000000 R12: ffffffff81a6e607
R13: ffff888062827d00 R14: 0000000000000046 R15: dffffc0000000000
FS:  00007f4921fbd640(0000) GS:ffff8881a2701000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555620b6e72 CR3: 000000002bede000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 __raw_spin_unlock_irqrestore home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/spinlock_api_smp.h:149 [inline]
 _raw_spin_unlock_irqrestore+0x1a/0x70 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock.c:194
 _test_bit home/wmy/Fuzzer/third_tool/linux-6.18/include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 cpumask_test_cpu home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:646 [inline]
 cpu_online home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:1205 [inline]
 __do_trace_hrtimer_setup home/wmy/Fuzzer/third_tool/linux-6.18/include/trace/events/timer.h:193 [inline]
 hrtimer_try_to_cancel+0x167/0x2f0 home/wmy/Fuzzer/third_tool/linux-6.18/include/trace/events/timer.h:193
 hrtimer_try_to_cancel home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1352 [inline]
 hrtimer_cancel+0x17/0x50 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1481
 drm_vblank_disable_and_save+0x283/0x3e0
 drm_crtc_vblank_off+0x317/0x990
 crtc_disable+0x405/0x620
 drm_atomic_helper_commit_modeset_disables+0x28/0x60
 vkms_atomic_commit_tail+0x4d/0x250
 commit_tail+0x293/0x410
 drm_atomic_helper_commit+0x30a/0x390
 drm_atomic_commit+0x233/0x300
 drm_atomic_connector_commit_dpms+0x3fc/0x4f0
 set_property_atomic+0x222/0x350
 drm_mode_obj_set_property_ioctl+0x413/0x5c0
 drm_connector_property_set_ioctl+0x100/0x160
 drm_ioctl_kernel+0x1ed/0x3e0
 drm_ioctl+0x574/0xb90
 vfs_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:51 [inline]
 __do_sys_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:597 [inline]
 __se_sys_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18f/0x210 home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:583
 do_syscall_64+0xcb/0xfa0 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_64.c:99
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f49211b059d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4921fbcf98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f4921425fa0 RCX: 00007f49211b059d
RDX: 00002000000003c0 RSI: 00000000c01064ab RDI: 0000000000000003
RBP: 00007f492124e078 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4921426038 R14: 00007f4921425fa0 R15: 00007f4921f9d000
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10501 jiffies! g240157 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=82244
rcu: rcu_preempt kthread starved for 10502 jiffies! g240157 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:I stack:28024 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 sched_info_arrive home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/stats.h:267 [inline]
 sched_info_switch home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/stats.h:330 [inline]
 prepare_task_switch home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:5122 [inline]
 context_switch home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:5272 [inline]
 __schedule+0x1044/0x5bb0 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:6929
 __schedule_loop home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:7011 [inline]
 schedule+0xe7/0x3a0 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:7026
 schedule_timeout+0x113/0x280 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/sleep_timeout.c:98
 rcu_gp_fqs_check_wake home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2007 [inline]
 rcu_gp_fqs_loop+0x18c/0xa00 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x26f/0x370 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2280
 kthread+0x3d0/0x780 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/kthread.c:463
 ret_from_fork+0x676/0x7d0 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/process.c:195
 ret_from_fork_asm+0x1a/0x30 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 2 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 62588 Comm: syz.0.16277 Not tainted 6.18.0 #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:native_queued_spin_lock_slowpath+0x23e/0x9c0
Code: 02 48 89 e8 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85 1c 07 00 00 b8 01 00 00 00 66 89 45 00 e9 c2 fe ff ff 89 44 24 40 f3 90 <e9> 5e fe ff ff 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03
RSP: 0018:ffffc900000076c0 EFLAGS: 00000002
RAX: 0000000000000001 RBX: 0000000000000001 RCX: ffffffff8b43f32e
RDX: ffffed1020f7ac6b RSI: 0000000000000004 RDI: ffff888107bd6350
RBP: ffff888107bd6350 R08: 0000000000000000 R09: ffffed1020f7ac6a
R10: ffff888107bd6353 R11: 0000000000000001 R12: 1ffff92000000eda
R13: 0000000000000003 R14: ffffed1020f7ac6a R15: ffffc90000007700
FS:  000055556b492500(0000) GS:ffff8880cf001000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4921fbcfc8 CR3: 000000012835c000 CR4: 00000000000006f0
Call Trace:
 <IRQ>
 debug_spin_lock_before home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock_debug.c:87 [inline]
 do_raw_spin_lock+0x20d/0x2b0 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock_debug.c:115
 __raw_spin_lock_irqsave home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x45/0x60 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock.c:162
 drm_handle_vblank+0x125/0xc70
 vkms_vblank_simulate+0xa8/0x390
 __run_hrtimer home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1779 [inline]
 __hrtimer_run_queues+0x1f5/0xb30 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x39a/0x880 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1912
 instrument_atomic_read home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/instrumented.h:68 [inline]
 _test_bit home/wmy/Fuzzer/third_tool/linux-6.18/include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 cpumask_test_cpu home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:646 [inline]
 cpu_online home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:1205 [inline]
 __do_trace_local_timer_exit home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/trace/irq_vectors.h:40 [inline]
 trace_local_timer_exit home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/trace/irq_vectors.h:40 [inline]
 __sysvec_apic_timer_interrupt+0x10d/0x400 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/apic/apic.c:1059
 instr_sysvec_apic_timer_interrupt home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/apic/apic.c:1052 [inline]
 sysvec_apic_timer_interrupt+0x54/0xc0 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/apic/apic.c:1052
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/idtentry.h:697
RIP: 0010:e1000_clean+0xeda/0x2810 home/wmy/Fuzzer/third_tool/linux-6.18/drivers/net/ethernet/intel/e1000/e1000_main.c:3822
Code: fa 48 c1 ea 03 80 3c 02 00 0f 85 0d 18 00 00 48 8b 4c 24 40 ba 9d 00 00 00 48 8b 81 60 02 00 00 48 89 04 24 89 90 d0 00 00 00 <48> 8b 81 60 02 00 00 8b 40 08 e8 97 8a 52 fb 8b 84 24 e8 00 00 00
RSP: 0018:ffffc90000007c00 EFLAGS: 00000246
RAX: ffffc90006c60000 RBX: 0000000000000000 RCX: ffff888102781070
RDX: 000000000000009d RSI: ffffffff8667cd18 RDI: ffff8881027812d0
RBP: ffff8881027816b8 R08: 0000000000000000 R09: ffffed10204f02d7
R10: 0000000000000000 R11: ffffffff9ab1e160 R12: 0000000000000001
R13: ffff888102780ffa R14: 0000000000004e20 R15: ffff888102780ff0
 __napi_poll.constprop.0+0xb9/0x540 home/wmy/Fuzzer/third_tool/linux-6.18/net/core/dev.c:7594
 net_rx_action+0x92d/0xe00 home/wmy/Fuzzer/third_tool/linux-6.18/net/core/dev.c:7746
 _test_bit home/wmy/Fuzzer/third_tool/linux-6.18/include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 cpumask_test_cpu home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:646 [inline]
 cpu_online home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:1205 [inline]
 trace_softirq_exit home/wmy/Fuzzer/third_tool/linux-6.18/include/trace/events/irq.h:142 [inline]
 handle_softirqs+0x1d4/0x870 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/softirq.c:623
 __irq_exit_rcu+0x109/0x170 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/bitops.h:202
 irq_exit_rcu+0x9/0x30 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/softirq.c:738
 common_interrupt+0xf7/0x110 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/irq.c:337
 </IRQ>
 <TASK>
 asm_common_interrupt+0x26/0x40 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/idtentry.h:688
RIP: 0010:lock_acquire+0x63/0x340 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/lockdep.c:5872
Code: 20 eb 11 83 f8 07 0f 87 b0 01 00 00 89 c0 48 0f a3 05 21 40 ce 0e 0f 82 68 01 00 00 8b 35 59 70 ce 0e 85 f6 0f 85 8d 00 00 00 <48> 8b 44 24 30 65 48 2b 05 38 20 eb 11 0f 85 c0 02 00 00 48 83 c4
RSP: 0018:ffffc9000352f3c0 EFLAGS: 00000206
RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000068c1bacb
RDX: 0ac0d5affe09d4ff RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffffff8e1c7aa0 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 page_ext_get+0x37/0x1b0
 __reset_page_owner+0x2b/0x1b0
 page_pool_page_is_pp home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/mm.h:4311 [inline]
 page_expected_state home/wmy/Fuzzer/third_tool/linux-6.18/mm/page_alloc.c:1039 [inline]
 free_page_is_bad home/wmy/Fuzzer/third_tool/linux-6.18/mm/page_alloc.c:1078 [inline]
 free_pages_prepare home/wmy/Fuzzer/third_tool/linux-6.18/mm/page_alloc.c:1369 [inline]
 free_unref_folios+0xa06/0x14e0 home/wmy/Fuzzer/third_tool/linux-6.18/mm/page_alloc.c:2958
 folios_put_refs+0x4b3/0x750 home/wmy/Fuzzer/third_tool/linux-6.18/mm/swap.c:159
 shmem_undo_range+0x54e/0x1210 home/wmy/Fuzzer/third_tool/linux-6.18/mm/shmem.c:1096
 inode_set_mtime_to_ts home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/fs.h:1838 [inline]
 shmem_truncate_range home/wmy/Fuzzer/third_tool/linux-6.18/mm/shmem.c:1232 [inline]
 shmem_evict_inode+0x39d/0xb90 home/wmy/Fuzzer/third_tool/linux-6.18/mm/shmem.c:1359
 hlist_unhashed home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/list.h:962 [inline]
 inode_unhashed home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/fs.h:938 [inline]
 remove_inode_hash home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/fs.h:3421 [inline]
 evict+0x3ce/0x8f0 home/wmy/Fuzzer/third_tool/linux-6.18/fs/inode.c:818
 iput.part.0+0x5e5/0xa20
 might_resched home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/kernel.h:61 [inline]
 iput+0x35/0x40 home/wmy/Fuzzer/third_tool/linux-6.18/fs/inode.c:1928
 dentry_unlink_inode+0x296/0x470 home/wmy/Fuzzer/third_tool/linux-6.18/fs/dcache.c:466
 __dentry_kill+0x1d2/0x600 home/wmy/Fuzzer/third_tool/linux-6.18/fs/dcache.c:669
 dput.part.0+0x4b0/0x9b0 home/wmy/Fuzzer/third_tool/linux-6.18/fs/dcache.c:911
 dput+0x1f/0x30 home/wmy/Fuzzer/third_tool/linux-6.18/fs/dcache.c:901
 __fput+0x516/0xb50 home/wmy/Fuzzer/third_tool/linux-6.18/fs/file_table.c:476
 task_work_run+0x16b/0x260 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/task_work.c:227
 exit_task_work home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/task_work.h:40 [inline]
 do_exit+0x85a/0x2b70 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/exit.c:966
 do_group_exit+0xd3/0x2a0 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/exit.c:1107
 __do_sys_exit_group home/wmy/Fuzzer/third_tool/linux-6.18/kernel/exit.c:1118 [inline]
 __se_sys_exit_group home/wmy/Fuzzer/third_tool/linux-6.18/kernel/exit.c:1116 [inline]
 __x64_sys_exit_group+0x3e/0x50 home/wmy/Fuzzer/third_tool/linux-6.18/kernel/exit.c:1116
 x64_sys_call+0x18c5/0x18d0 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_64+0xcb/0xfa0 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_64.c:99
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f34a6db059d
Code: Unable to access opcode bytes at 0x7f34a6db0573.
RSP: 002b:00007ffc4699cd08 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f34a6db059d
RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ffc4699cd80 R08: 0000000000000000 R09: 0000000000000032
R10: 0000001b2e920a18 R11: 0000000000000202 R12: 0000000000000030
R13: 0000000000000032 R14: 00007ffc4699cdf0 R15: 000000000020a5d3
 </TASK>

Best regards, 
Zhi Wang